1. Field of the Invention
The present invention relates to a method for controlling a penetration bead in an automatic one-side gas shielded arc welding.
2. Description of the Prior Art
A prior art automatic one-side gas shielded arc welding method is shown in FIG. 1. Backing material 2 comprising solid flux or ceramics is adhered to the back of work pieces 1 along a weld line by a backing copper plate 3. Backing material 2 melts during welding and turns into slag 4 which protects a penetration bead. An electric current is sent to electrode wire 5 through electrode tip 7. Electrode wire 5 is fed continuously by feed roller 6. The welding is effected by arc 10 being generated in an atmosphere of shielding gas 9 which is supplied from gas nozzle 8. A welding apparatus is moved by a travelling carriage (not shown) in the direction of the welding as the welding goes on.
The prior art automatic one-side gas shielded arc welding method as mentioned above is used widely for welding a structure which can not be turned over. In this case, however, non-uniformity of the penetration bead occurs due to the differences of root gap. In order to remove such defects, the following two methods have been used:
(a) Weld parameters such as a welding speed are change by manual control of a worker during the welding.
(b) The root gap of the portions to be welded is formed very accurately in advance.
The first method requires a high skill. For example, when a giant structure such as a ship is welded with an automatic one-side gas shielded arc welding method, it is impossible to observe the back of a welded portion and to grasp the conditions thereof. Therefore, the worker relies upon his experience and individual workmanship. Accordingly, the formation of a uniform penetration bead is attended with difficulties and requires an accumulated high skill. The second method has disadvantages in that it is difficult to maintain the accuracy necessary for a giant structure because the required accuracy of the root gap is approximately .+-.1 mm.